1. Field of the Invention
This invention relates to autogyro aircraft, components thereof and control systems therefor.
2. State of the Art
An autogyro aircraft derives lift from an unpowered, freely rotating rotary wing or plurality of rotary blades. The energy to rotate the rotary wing results from the forward movement of the aircraft in response to a thrusting engine such as a motor driven propeller.
During the developing years of aviation aircraft, autogyro aircraft were proposed to avoid the problem of aircraft stalling in flight and to reduce the need for runways. The relative airspeed of the rotating wing is independent of the forward airspeed of the autogyro, allowing slow ground speed for takeoff and landing, and safety in slow-speed flight. Engines may be tractor-mounted on the front of an autogyro or pusher-mounted on the rear of the autogyro.
Airflow passing the rotary wing, alternately called rotor blades, which are tilted upwardly toward the front of the autogyro, provides the driving force to rotate the wing. The Bernoulli effect of the airflow moving over the rotary wing surface creates lift.
Various autogyro devices in the past have provided some means to begin rotation of the rotary wing prior to takeoff, thus further minimizing the takeoff run down a runway.
U.S. Pat. No. 1,590,497 issued to Juan de la Cierva of Madrid, Spain, illustrated a very early embodiment of an autogyro. Subsequently, de la Cierva obtained U.S. Pat. No. 1,947,901 which recognized the influence of the angle of attack of the blade of a rotary wing. The optimum angle of attack for the blades or rotary wing was described by Pitcairn in U.S. Pat. No. 1,977,834 at about the same time. In U.S. Pat. No. 2,352,342, Pitcairn disclosed an autogyro with blades which were fully hinged relative to the hub.
Even though the principal focus for low speed flight appears to have shifted to helicopters, there appears to have been some continuing interest in autogyro craft. However, development efforts appear to have largely been restricted to refinements of the early patented systems. For instance, Salisbury, et al., U.S. Pat. No. 1,838,327, showed a system to change the lift to drag response of a rotary wing but did not change the actual angle of attack of the rotor blade.
Later, U.S. Pat. No. 4,092,084 (Barltrop) disclosed a system in which the rotor blade angle with respect to a longitudinal axis was allowed to teeter. As the teeter motion occurred, a linkage coupling the two rotor blades together tended to change the angle of attack of the blades. That is, the rotor blade pitch angle varied with the rotation rate. Again, no operator control was allowed but only a variation between set limits to facilitate spinning the rotary wing up to takeoff speeds. Similarly, U.S. Pat. No. 3,149,802 (Wigal) shifts blade pitch between two angular positions dependent upon the rate of rotation. Finally, U.S. Pat. No. 3,465,705 (Bensen) discloses a system for diverting engine power to prerotate the rotary wing up to takeoff speed. The rotor blades change their angle of attack between limits according to the rate of rotation of the rotor.
In all of the foregoing patents, it appears that blade pitch varied between two positions: a spin up position; and a flight position. U.S. Pat. No. 2,183,119 (Larsen) employed yet another method to actuate a change in pitch from a no-lift position to a maximum-lift position by coupling a hydraulic pump to the rotation of the rotor. The hydraulic pressure developed operated several devices on the aircraft including a switch of the angle of attack of the rotor blades, between two positions.
In summary, none of the autogyro aircraft known to applicants have addressed the continuously variable control of angle of attack of the rotor blade in flight. The result of continuously variable control of the angle of attack of the rotor blade in flight, sometimes called collective pitch, is that the angle of attack can be low for spinning the blades up to takeoff speed, and then changed for maximum lift. Later, in flight at higher speeds, the angle of attack of the blades of the rotary wing is again reduced to minimize drag and allow maximum flight speed, the lift being easily adequate at such speeds.
The prior art suffers from poor spin up characteristics, traded off against takeoff characteristics traded off against flight drag characteristics. Even aircraft which allowed multiple angles of attack did not allow smooth variation between the minimum and maximum values, nor effective control of the transition therebetween. In the prior art, the blades' angle of attack is typically too large, resulting in excessive drag, for efficient spinup to takeoff speeds, yet is too small for effective lift at moderate speeds. Then, as an aircraft increases forward speed, the angle of attack of the blades is too large for maximum cruising speeds, causing excessive drag. The instant invention allows infinite variation in the blades' angle of attack to create the best performance in any conditions.
Blade angle of attack is distinguishable from rotary wing angle of attack. The latter refers to the angle of the plane of motion of the entire rotary wing with respect to the relative wind passing over the aircraft. The former, as described, is the angle which the chord of an individual blade makes with respect to the relative wind. However, blade angle of attack is usually described herein from a grounded position of the aircraft so that the angle is measured between the chord and the path of the rotating blade.